The invention relates generally to semiconductor processing and, more particularly, to a semiconductor wafer clamping apparatus and method.
A number of semiconductor processes may cause unwanted heating of wafers. Such heating may be undesirable because, for example, it can result in uncontrolled diffusion of dopants within the wafer and can degrade patterned photoresist layers. To limit this type of heating, wafers may be cooled during certain semiconductor processes.
In particular, certain ion implantation processes may utilize wafer cooling. Ion implantation is a conventional technique for introducing dopants into semiconductor materials. A desired dopant material is ionized in an ion source and the ions are accelerated to form an ion beam of selected energy which is directed at the surface of the wafer. The ions in the beam penetrate into the bulk semiconductor material to form a region of the desired conductivity. The impingement of the energetic ions upon the wafer can heat the wafer which, in some cases, increases the wafer temperature enough to cause the undesirable effects described above, if the wafer is not cooled. Cooling may be particularly important in ion implantation processes having high implant energies, long implant times, and/or high implant doses.
Wafer cooling may be challenging in vacuum environments, such as those used in ion implantation processes, due to the absence of convection cooling and limited cooling via gas-phase conduction. In some processes, wafers are cooled by cooling a supporting structure to which the wafer is clamped. In these processes, heat is conducted away from the wafer as a result of its contact with the cooled structure. However even when the wafer and supporting structure are highly polished, direct contact between the wafer and supporting structure may only occur in localized areas due to surface roughness on the microscopic level and/or contamination. As a result, conduction in these cases may not be highly efficient.
Conventional clamping techniques for holding a wafer to the supporting structure including mechanical clamping, electrostatic clamping, or centrifugal clamping. In some of these conventional clamping techniques, contamination may be generated as a result of the direct contact between the wafer and the supporting structure. It is generally advantageous to limit such contamination, which can degrade device performance.
Accordingly, a need exists for wafer clamping apparatus which may be used to hold and efficiently cool a wafer during semiconductor processing and, in particular, during ion implantation.
The invention provides a wafer clamping apparatus and method for use in semiconductor processing. The apparatus includes a clamping component that holds a backside of the wafer to a supporting surface and cools the wafer to prevent overheating. The clamping component is a chemical compound, such as H2O, that covers at least a section of the supporting surface and can adhere the backside of the wafer to the supporting surface. The component undergoes one or more phase-changes (e.g., liquid to solid, solid to liquid, etc.) to facilitate various operations throughout the process. The phase-changes ensure that the wafer may be easily loaded onto and released from the supporting structure at the beginning and end of the process, respectively, while being securely held and cooled during the process. The wafer clamp is suitable for use in a number of semiconductor processes, including ion implantation, and is particularly useful in processes that require wafer cooling such as ion implantation processes that have high implant energies, long implant times, high implant doses, or combinations thereof.
In one aspect, the invention provides a wafer clamping apparatus. The apparatus includes a platen having a supporting surface, and a clamping component that covers at least a section of the supporting surface and undergoes at least one phase-change during a processing cycle to effect the clamping of a wafer to the supporting surface.
In another aspect, the invention provides a wafer clamping apparatus. The apparatus includes a platen having a supporting surface, and a clamping component covering at least a section of the supporting surface. The clamping component is adherable to a backside of a wafer and capable of releasing a backside of a wafer in response to an increase in temperature.
In another aspect, the invention provides a wafer clamping apparatus. The apparatus includes a platen having a supporting surface. The apparatus further includes a clamping component that during a first period of a processing cycle, is a liquid film covering at least a portion of the supporting surface and, during a second period of the processing cycle, is a solid film adherable to a backside of a wafer.
In another aspect, the invention provides a method of clamping a wafer. The method includes providing a clamping component covering at least a section of a supporting surface of a platen, and changing the phase of the clamping component to effect the clamping of a wafer to the supporting surface.
In another aspect, the invention provides a method of clamping a wafer. The method includes providing a solid film on at least a portion of a supporting surface of the platen to adhere a backside of the wafer to the supporting surface. The method further includes heating the solid film to release the backside of the wafer from the supporting surface.
Among other advantages, the clamping apparatus is capable of securely holding a wafer which permits the wafer to be moved as desired during processing. The clamping apparatus also provides highly efficient cooling in vacuum due to the large contact area between the clamping component and the wafer, and the relatively high thermal conductivity of the clamping component. Furthermore, the clamping apparatus may reduce the contamination generated as compared to certain conventional clamping techniques, which involve direct contact between the wafer and the supporting surface, due to the presence of the clamping component between the wafer and the supporting surface.
Other advantages, features, and embodiments will be apparent from the following detailed description when considered in conjunction with the accompanying figures.